Frank Hinze

Dependence of ultrasonic attenuation on the material properties

Abstract Ultrasonic spectroscopy is a promising measurement technique for the characterisation of emulsions and suspensions over a wide range of particle size and concentration. It appears highly suitable for on-line applications, in particular for dense nano-sized particle systems, where the system stability may be very sensitive to changes in the concentration. In the case of colloidal dispersions the particle sizes are usually smaller than the sound wavelength. Then dissipative processes rather than scattering govern the acoustic behaviour of such systems. The dissipative processes, however, are affected by several material properties, whose significance for the overall acoustic behaviour depends on the type of the material system, e.g. thermal properties are important in the case of emulsions and non-watery suspensions but not for watery suspensions. Often the information on these parameters is incomplete and not sufficiently accurate. In this paper the stability of ultrasonic particle size measurement against incorrect values of the relevant material properties is investigated. This was done firstly by analytical consideration. From this, the degree of influence of the respective material properties on the analysis of spectrometric measurements was derived for oil-water-emulsions, watery and non-watery suspensions. It could be shown that the single properties affect the analysis very differently. In a second step, the conclusions obtained analytically could be confirmed by analysing experimental attenuation spectra with slightly changed material property data. The paper is intended to give users of ultrasonic spectroscopy a practical guide for deciding which material properties have to be obtained with high accuracy and which can be estimated.

Ultrasonic Spectrometry for Particle Size Analysis in Dense Submicron Suspensions

Ultrasonic spectrometry was applied to the particle size analysis of disperse systems. The investigations were made for acoustic conditions called the long-wavelength regime (LWR). In the LWR the acoustic behaviour is governed by dissipative effects rather than by scattering. Two principal theoretical approaches to ultrasonic spectrometry — scattering theory and coupled phase models — are introduced. A model based on a newly developed coupled phase model and the scattering theory (ECAH theory) is implemented in the ultrasonic spectrometer Acousto Phor. Experiments were carried out for several suspensions with a high density contrast. It could be demonstrated that the model successfully describes acoustic attenuation and that the inversion algorithm finds particle size distributions comparable to those given by other measurement techniques. With regard to the particle size, a lower and an upper limit for the applicability were determined, which include three decades. As a further result, the model was validated at concentrations up to 10 vol.%. The model is considered to be open to development to cover even higher concentrations.

Charakterisierung von Suspensionen nanoskaliger Partikel mittels Ultraschallspektroskopie und elektroakustischer Methoden

Die technische Beherrschung von Dispersionen mit Partikeln im Grosenbereich von Nanometern verspricht einen Innovationsschub fur einige industrielle Branchen. Voraussetzung fur die Entwicklung entsprechend neuer Produkte ist die sichere Charakterisierung der dispersen Stoffsysteme. Eine Charakterisierung sollte immer auch die Bestimmung der Partikelgrosenverteilung beinhalten, da an sie haufig die spezifische Wirkung dieser Stoffsys teme gekoppelt ist. Ultraschallmesstechnik und Elektroakustik sind zwei der wenigen verfugbaren Messtechniken, die es ermoglichen, die Grosenverteilung und das Zetapotential von Partikeln mit Abmessungen bis hinunter zu 10 nm zu bestimmen. Ein weiterer wesentlicher Vorteil dieser Methoden ist die Moglichkeit, auch Messungen in hochkonzentrierten Stoffsystemen durchzufuhren. Der vorliegende Bericht beschreibt die Ultraschallspektroskopie zur Vermessung von fein- und feinstdispersen festen Partikeln und die zur Auswertung der Messsig nale bekannten theoretischen Ansatze. Auserdem wird uber Erfahrungen im Umgang mit der derzeit verfugbaren Messtechnik berichtet. Characterization of Suspensions of Nanoscale Particles by Means of Ultrasound Spectroscopy and Electroacoustic Methods Technical control over dispersions with particles in the nanometer size realm should bring about a boost in innovations for some parts of industry. Requirements for the development of these new products is the accurate characterization of the various materials systems. A characterization should always include a determination of the particle size distribution, since it is coupled to the specific effects of these systems. Ultrasound measurement techniques and electroacoustics are two if the available techniques that allow determination of the size distribution and zeta potential of particles with dimensions up to 10 nanometers. A further fundamental advantage of the method is the possibility of carrying out measurements in high-concentration materials systems. This report describes ultrasound spectroscopy for the measurement of fine- and very-fine-dispersion particles, and the known theoretical concepts for the interpretation of spectra. In addition, experiences in the use of currently available measurement techniques are presented.

Dynamische Extinktionsspektroskopie – Eine Chance zur Erweiterung des Messbereiches photometrischer Partikelmesstechniken

Dynamic extinction spectroscopy is based on the simultaneous application of dynamic extinction measurement and optical extinction spectroscopy for online particle size measurement. It covers a range of particle sizes and size distributions from approx. 80 nm to 250 pm. Different applications will underline the potential of this measuring method for online process control.